Plant community effects on the diversity and pathogen suppressive activity of soil streptomycetes

Ecological factors that promote pathogen suppressive microbial communities remain poorly understood. However, plants have profound impacts on the structure and functional activities of soil microbial communities, and land-use changes which alter plant diversity or community composition may indirectly affect the structure and function of microbial communities. Previous research has suggested that the streptomycetes are significant contributors to pathogen suppression in soils. We compared soil streptomycete communities from high and low plant diversity treatments using an experimental manipulation that altered plant diversity while controlling for soil structure and disturbance. Specifically, we characterized an isolate collection for inhibition of plant pathogens as a measure of functional activity, and for 16S rDNA sequence to measure community structure. In this system, high and low diversity plant communities supported streptomycete communities with similar diversity, phylogenetic composition, and pathogen suppressive activity. However, inhibitory phenotypes differed among treatments for several phylogenetic groups, indicating that local selection is leading to divergence between streptomycetes from high and low plant diversity communities. Although the ability to inhibit plant pathogens was common among soil streptomycetes, pathogen-inhibitory activity differed widely among phylogenetic groups. The breadth and intensity of pathogen inhibition by soil streptomycetes were positively related.